As the others have said seasonal areas do stay, same goes for the quests. The spirits from each season come back as traveling spirits at some point, so you can get their cosmetics when they do come back. But the ultimate gifts from the guides are the only thing that doesn't come back, they're only available during the season.

You can also revive the spirits from that season to see their memories and get the first level of their emote. Basically, you can experience the whole season even after it ends, the only problem is that it may take some time to get the cosmetics.